Network managers and other technology specialists must often manage complex networks. These networks include numerous components such as switches, routers, gateways and terminating equipment such as work stations, personal computers (PCs), servers, and the like.
Some computer software systems exist to analyze and diagram elements of a network. Examples of such systems are Visio Enterprise™ by Visio Corporation and OpenView™ by Hewlett-Packard Corporation. These systems analyze a network to create a database that logically represents the various components in the network. These systems can then create a diagram of that network using the database.
Certain network components or circuits are particularly difficult to analyze, such as frame relay circuits. Frame relay circuits employ specialized devices, known as frame relay access devices (FRADs) that encapsulate any native protocol data unit (PDU). Thus, frame relay circuits can encapsulate various size data packets associated with any native PDU and packetize it for transmission over permanent virtual circuits (PVCs). PVCs are predetermined paths specifically defined in frame relay routing logic. Telecommunication service providers favor frame relay circuits since they can provide numerous subscribers to their telecommunication networks without adding additional infrastructure. Frame relay circuits are typically intended for data communication applications especially for networking local area networks (LANs) where data transmissions are bursty.
When analyzing a network containing frame relay circuits, the above software systems simply discover data link connection identifiers (DLCIs), also known as data link circuit identifiers. DLCIs are 10-bit portions of address fields prepended to each frame transmitted along predetermined frame relay circuits. For example, if a device identified and analyzed under the Visio Enterprise System identifies a router having frame relay capability, the system identifies the particular port of the router having frame relay capability and identifies individual DLCIs associated with that port. Each DLCI can be thought of as a single direction pipe. Data may flow into or out of the pipe. Thus, each DLCI defines either a front end of the pipe or a back end. Each frame relay port is attached, through a public switched network to another frame relay port, somewhere else in the world, with each port having unique DLCIs.
Each router port, having one or more associated DLCI, has no information about the other end of the frame relay circuit; the other end is the other frame relay port on another router somewhere in the network. Since neither router has information identifying the other router, the above software systems cannot determine which DLCIs are connected to other DLCIs within the network.
Network managers typically must know the DLCI connection pairs for diagnostic and usage purposes. Therefore, if the network includes frame relay circuits, then the network manager typically must rely on data from the frame relay circuit providers, or purchase proprietary frame relay hardware (FRADs), which is more expensive and less common than standard router hardware. The FRADs, or “probes”, are capable of analyzing frame relay circuits, but the network manager must continue to use such expensive hardware in the future if additional frame relay circuits are added, or purchase improved hardware if increased functionality is desired.